Method for monitoring film thickness, a system for monitoring film thickness, a method for manufacturing a semiconductor device, and a program product for controlling film thickness monitoring system

ABSTRACT

A method monitors a thickness of a subject film deposited on an underlying structure, the underlying structure contains at least one thin film formed on a substrate. The method includes determining thickness data of the underlying structure and storing the thickness data of the underlying structure in a thickness memory; measuring profile of optical spectrum of the subject film on the underlying structure; reading the thickness data of the underlying structure from the thickness memory; calculating theoretical profiles of the optical spectrum of the subject film based upon corresponding candidate film thicknesses of the subject film and the thickness data of the underlying structure; and searching a theoretical profile of the subject film, which is closest to the measured profile of optical spectrum of the subject film so as to determine a thickness of the subject film.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 10/933,441, filed Sep. 3,2004, now U.S. Pat. No. 7,348,192 which is incorporated herein byreference.

This application claims benefit of priority under 35 USC 119 based onJapanese Patent Application No. P2003-314626 filed Sep. 5, 2003, theentire contents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a computer implemented monitoringmethod for measuring a thickness of a thin film in a multi-layerstructure. The present invention particularly relates to the method formeasuring film thickness using computer integrated manufacturing (CIM)system, a sub system for measuring film thickness in the CIM system.Further, the present invention pertains to control programs forcontrolling the sub systems for measuring film thickness. Further, thepresent invention relates to a method of manufacturing a semiconductordevice using in-line monitoring according to this method for measuringfilm thickness.

2. Description of the Related Art

As degree of integration density of semiconductor integrated circuitssuch as large-scale integrations (LSIs) becomes higher, the number ofwiring layers in a multi-level interconnection become larger and larger.In a case in which there are eight metallic wiring layers, it may begeneral to deposit around thirteen to fourteen interlayer insulationfilms, which must be formed corresponding number of production stages.Thus in-line monitoring of film thickness of multi-layer structure isextremely important.

The earlier procedure of measuring film thickness of three-layersstacked structure by using a light interference type thickness-measuringtool will be described as a simple example, using flowcharts of FIGS. 1to 3, and the data flow diagrams of FIG. 4.

(a) First, in a step S901, a first film is formed on a substrate. Nextin a step S902, using a thickness-measuring tool 6, white incident lightis irradiated onto the substrate having the first film formed thereon.In a step S903, the thickness-measuring tool 6 disperses light reflectedfrom the substrate into its component wavelengths using a spectroscopeand detects the intensity of the reflected light at each resolvedwavelength using a photo detector. Further, in a step S904, a sequenceof light intensity data detected by the photo detector are stored so asto establish a profile (x: wavelength, y: intensity) of an actualmeasured reflection spectrum by a control computer of thethickness-measuring tool 6. The interference of light waves, which havebeen reflected at the front and back side of the first film (at twoboundaries with different optical densities) leads to periodicalamplifications and extinction in the spectrum of a white continuumlight. For example, plotting the actual measured wavelength along theabscissa and reflected light intensity along the ordinate, in awavelength range of 200 nm to 800 nm, there is a serpentine profilehaving two peaks and two valleys.

(b) Next, in a step S905, a plurality of theoretical profiles of thereflection spectrums are calculated at the first film's thickness range(ta˜ta+Δta) registered in a first measurement recipe of the controlcomputer of the thickness-measuring tool 6. Further, in a step S906, oneof the profiles closest to the profile of the actual measured reflectionspectrum of the first film attained in the step S904 is searched in thetheoretical profiles of the reflection spectrums arithmeticallycalculated in the step S905. Then the thickness value, upon which theclosest theoretical profile of the reflection spectrum to the actualmeasured reflection spectrum is derived, is determined as the filmthickness T_(A). Afterward, in a step S907, this film thickness value isexpressed as a film thickness value T_(A, L1, W1) of specific lots andwafers (Further, the film thickness value T_(A, L1, W1) is stored awayin a management server 9, as shown in FIG. 4).

(c) In a step S911 of FIG. 2, a second film is formed on the first film.Next, in a step S912, using the thickness-measuring tool 6, whiteincident light is irradiated onto the substrate having the second filmformed thereon. In a step S913, the thickness-measuring tool 6 disperseslight reflected from the substrate using the spectroscope and detectsthe intensity of the reflected light at each resolved wavelength using aphoto detector. Further, in a step S914, a sequence of light intensitydata detected by the photo detector are stored so as to establish aprofile of an actual measured reflection spectrum by the controlcomputer of the thickness-measuring tool 6. The profile of the actualmeasured reflection spectrum represents the reflection at the boundaryof the first and second films and the reflection at the boundary of thesubstrate and the first film, and expresses a complex serpentineprofile. Although results depend upon the relationships of the materialparameters and film thickness, plotting the actual measured wavelengthalong the abscissa and reflected light intensity along the ordinate, ina wavelength range of 200 nm to 800 nm there is generally a serpentineprofile having three to four peaks and three to four valleys.

(d) In a step S915, a plurality of theoretical profiles of thereflection spectrums are calculated. Here, in addition to the secondfilm's thickness range (tb˜tb+Δtb) registered in a second measurementrecipe of the control computer of the thickness-measuring tool, thethickness range (ta˜ta+Δta) of the first film which is underneath thesecond film, must be included in the calculation. Next, in a step S916,one of the profiles closest to the actual measured reflection spectrumof the second film attained in the step S914 is searched in thetheoretical profiles of the reflection spectrums arithmeticallycalculated in the step S915. Then the thickness value, upon which theclosest theoretical profile of the reflection spectrum to the actualmeasured reflection spectrum is derived, is determined as the filmThickness T_(B). Afterward, in a step S917, this film thickness value isexpressed as a film thickness value T_(B, L1, W1) of specific lots andwafers (Further, the film thickness value T_(B, L1, W1) is stored awayin a management server 9, as shown in FIG. 4).

(e) In a step S921 of FIG. 3, a third film is formed on the second film.Next, in a step S922, using the thickness-measuring tool 6, whiteincident light is irradiated onto the substrate having the third filmformed thereon. In a step S923, the thickness-measuring tool 6 disperseslight reflected from the substrate using the spectroscope and detectsthe intensity of the reflected light at each resolved wavelength using aphoto detector. Further, in a step S924, a sequence of light intensitydata detected by the photo detector are stored so as to establish aprofile of an actual measured reflection spectrum by the controlcomputer of the thickness-measuring tool 6. The actual measuredreflection spectrum represents the reflection at the boundary of thesubstrate and the first film, the reflection at the boundary of thefirst and second films, and the reflection at the boundary of the secondand third films, and expresses a complex serpentine profile. Althoughresults depend upon the relationships of the material parameters andfilm thickness, plotting the actual measured wavelength along theabscissa and reflected light intensity along the ordinate, in awavelength range of 200 nm to 800 nm there is generally a serpentineprofile having five peaks and five valleys.

(f) In a step S925, a plurality of theoretical profiles of thereflection spectrums are calculated. Here, in addition to the thirdfilm's thickness range (tc˜tc+Δtc) registered in a third measurementrecipe of the control computer of the thickness-measuring tool, thethickness range (ta˜ta+Δta) of the first film which is underneath thesecond film, and the thickness range (tb˜tb+Δtb) of the second filmwhich is underneath the third film must be included in the calculation.Next, in a step S926, one of the profiles closest to the actual measuredreflection spectrum of the third film attained in the step S924 issearched in the theoretical profiles of the reflection spectrumsarithmetically calculated in the step S925. Then the thickness value,upon which the closest theoretical profile of the reflection spectrum tothe actual measured reflection spectrum is derived, is determined as thefilm thickness T_(C). Afterward, in a step S927, this film thicknessvalue is expressed as a film thickness value T_(C, L1, W1) of specificlots and wafers (Further, the film thickness value T_(C, L1, W1) isstored away in a management server 9, as shown in FIG. 4).

As put forth above, for measuring the film thickness of layeredstructures by earlier technology, and even in cases of measuring thetopmost layer of a layered structure, the film thickness of theunderlying layer also had to he measured. Put simply, in cases having athree-layers structure that results after forming the second film on thefirst film and the third film on the second film, aside from measuringthe film thickness range (tc˜tc+Δtc) of the third film, theoreticalprofiles of the reflection spectrums for film thickness ranges of thefirst (ta˜ta+Δta) and second (tb˜tb+Δtb) thin films must also becalculated. So in this earlier methodology, compared with a measurementin which film thickness of a single layer is measured by calculatingtheoretical profiles of the reflection spectrums of the reflectionspectrum at a film thickness range (tc˜tc+Δtc) of a single layer in astructure such as the first film/substrate, in the measurement of amulti-layer structure, problems such as increased measurement time, anddecreased measurement precision (occurrence of “value jump”, etc.) willarise. In recent LSI, multi-layer structure above ten to thirteen layershave become the norm, and the calculation of all of the theoreticalprofiles of the reflection spectrums for film thickness ranges ofunderlying respective layers of these multi-layer structure uses upcomputer memory resources, bringing the need far an extremely longmeasurement time period.

Further, although it is also possible to insert dedicated extrasemiconductor wafers far the exclusive purpose of measuring respectivefilm thickness, and measure respective film thickness of thecorresponding level in each of the process steps in which each of thethin films is formed, but rising manufacturing costs, in themanufacturing generation in which high priced large diametersemiconductor wafers are employed, becomes problematic. In a situationhaving a multi-layer structure of above ten to thirteen layers,inserting extra semiconductor wafers within underlying films leads toserious increases in manufacturing costs, when switching over to a 200mm to 300 mm diameter semiconductor wafer.

Further, in a light interference type thickness-measuring methodology,it is impossible to measure precisely a multi-layer structureencompassing adjacent two layers, each having identical or extremelydose refraction indice, or it will generate a drop in precision of themeasurement.

SUMMARY OF THE INVENTION

An aspect of the present invention inheres in a method for monitoring athickness of a subject film deposited on an underlying structure, theunderlying structure contains at least one thin film formed on asubstrate. Namely, the method includes (a) determining thickness data ofthe underlying structure before the subject film is formed on theunderlying structure, and storing the thickness data of the underlyingstructure in a thickness memory, (b) measuring profile of opticalspectrum of the subject film after the subject film is formed on theunderlying structure, (c) reading the thickness data of the underlyingstructure from the thickness memory, (d) calculating a plurality oftheoretical profiles of the optical spectrum of the subject film basedupon corresponding candidate film thicknesses of the subject film, usinga measurement recipe for the subject film and the thickness data of theunderlying structure, and (e) searching one of the theoretical profilesof the optical spectrum of the subject film, which is closest to themeasured profile of optical spectrum of the subject film so as todetermine a thickness of the subject film by die closest theoreticalprofile.

Another aspect of the present invention inheres in a system formonitoring thickness of each layer in a multi-layer structure,encompassing (a) a thickness memory configured to store thickness dataof each layer of a underlying structure, disposed under a subject filmin the multi-layer structure, (b) an optical system configured to detectreflected light from a surface of the multi-layer structure, (c) aprofile memory configured to store measured profile of optical spectrumof the subject film, the measured profile of optical spectrum beingacquired by the optical system, (d) a measurement recipe memoryconfigured to store measurement recipes of each layer of the multi-layerstructure, (e) a calculation module configured to read thickness data ofthe underlying structure from the thickness memory, and calculate aplurality of theoretical profiles of the optical spectrum of the subjectfilm based upon corresponding candidate film thicknesses of the subjectfilm prescribed in the measurement recipe, far the subject film, and (f)a determination module configured to search one of the theoreticalprofiles of the optical spectrum of the subject film, which is closestto the measured profile of optical spectrum of the subject film so as todetermine a thickness of the subject film by the closest theoreticalprofile.

Still another aspect of the present invention inheres in a method formanufacturing a semiconductor device having multi-layer interconnection.Namely, the method includes (a) forming a first film on an underlyingstructure, the underlying structure contains at least one thin filmformed en a substrate, (b) determining thickness data of the first filmand storing the thickness data of the first film in a thickness memory,(c) forming a second film on the first film, (d) measuring profile ofoptical spectrum of the second film after the second film is formed onthe first film, (e) reading the thickness data of the first film and theunderlying structure from the thickness memory, (f) calculating aplurality of theoretical profiles of the optical spectrum of the secondfilm based upon corresponding candidate film thicknesses of the secondfilm, using a measurement recipe for the second film and the thicknessdata of the first film and the underlying structure, and (g) searchingone of the theoretical profiles of the optical spectrum of the secondfilm, which is closest to the measured profile of optical spectrum ofthe second film so as to determine a thickness of the second film by theclosest theoretical profile.

Still another aspect of the present invention inheres in a computerprogram product for controlling a monitoring system so as to monitor athickness of a subject film deposited on an underlying structure, theunderlying structure contains at least one thin film formed on asubstrate, the monitoring system has a thickness memory storing thethickness data of the underlying structure, the thickness data isdetermined before the subject film is formed on the underlyingstructure. Namely, the program includes (a) instructions configured tomeasure optical spectrum of the subject film formed on the underlyingstructure, (b) instructions configured to read the thickness data of theunderlying structure from the thickness memory, (c) instructionsconfigured to calculate a plurality of theoretical profiles of theoptical spectrum of the subject film based upon corresponding candidatefilm thicknesses of the subject film, using a measurement recipe for thesubject film and the thickness data of the underlying structure, and (d)instructions configured to search one of the theoretical profiles of theoptical spectrum of the subject film, which is closest to the measuredprofile of optical spectrum of the subject film so as to determine athickness of the subject film by the closest theoretical profile.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will be described withreference to the accompanying drawings. It is to be noted that the sameor similar reference numerals are applied to the same or similar partsand elements throughout the drawings, and the description of the same orsimilar parts and elements will be omitted or simplified. Generally andas it is conventional in the representation of film thickness-measuringtools, it will be appreciated that the various drawings are not drawn toscale from one figure to another nor inside a given figure, and inparticular that the layer thicknesses are arbitrarily drawn forfacilitating the reading of the drawings.

FIGS. 1 to 3 are flow charts showing an earlier thickness monitoringmethod;

FIG. 4 is a data flow diagram showing the operation of an earlierthickness monitoring system, which is adapted for executing in-linethickness monitoring of a three-layers structure;

FIG. 5 is a rough sketch showing a thickness monitoring system,illustrating principally a thickness-measuring tool employed in thesystem, according to a first embodiment of the present invention;

FIG. 6 is a data flow diagram showing the operation of the thicknessmonitoring system according to the first embodiment, which is adaptedfor executing in-line thickness monitoring of a three-layers structure;

FIG. 7A is a diagram showing the details of the data structure of thefilm thickness data of the first film, the data are stored in thethickness memory of the CIM server (measurement control server);

FIG. 7B is a diagram showing the details of the data structure of thefilm thickness data of the first and second films, the data are storedin the thickness memory of the CIM server;

FIG. 7C is a diagram showing the details of the data structure of thefilm thickness data of the first, second and third films, the data arestored in the thickness memory of the CIM server;

FIG. 8 is a diagram showing the details of the data structure of thefilm thickness data stored in the thickness memory of the CIM server,the data are sorted into corresponding measurement sites;

FIG. 9A is a diagram showing an example of actual measured reflectionspectrums (measured profile of optical spectrums) for the first filmstored in the profile memory of the measuring-tool-side computer in thethickness monitoring system according to the first embodiment;

FIG. 9B is a diagram showing an example of actual measured reflectionspectrums for the first and second films stored in the profile memory ofthe measuring-tool-side computer in the thickness monitoring systemaccording to the first embodiment;

FIG. 9C is a diagram showing an example of actual measured reflectionspectrums for the first, second and third films stored in the profilememory of the measuring-tool-side computer in the thickness monitoringsystem according to the first embodiment;

FIGS. 10 to 12 are flow charts describing a thickness monitoring method(in-line monitoring method) according to the first embodiment;

FIG. 13 is a rough sketch showing a thickness monitoring system,illustrating principally a thickness-measuring tool employed in thesystem, according to a modification of the first embodiment of thepresent invention;

FIG. 14 is a rough sketch showing the thickness monitoring system,illustrating principally the connection relationships with acommunication network, according to a second embodiment of the presentinvention;

FIG. 15 is a data flow diagram showing the operation of the thicknessmonitoring system according to the second embodiment, which is adaptedfor executing in-line thickness monitoring of a three-layers structure;

FIG. 16 is a rough sketch showing a thickness monitoring system,illustrating principally a third thickness-measuring tool employed inthe system with first and second thickness-measuring tools, according tothe second embodiment of the present invention;

FIG. 17A shows a wavelength dependence of the ratio (tan ψ) of theintensity of the P-polarized and the S-polarized reflected lightsmeasured by the third thickness-measuring tool (spectroscopicellipsometer) according to the second embodiment;

FIG. 17B shows a wavelength dependence of the phase difference (cos Δ)between the P-polarized and the S-polarized reflected lights measured bythe third thickness-measuring tool according to the second embodiment;

FIG. 18 is a flowchart showing the measurement procedure of the thirdthickness-measuring tool (spectroscopic ellipsometer) according to thesecond embodiment;

FIG. 19 is a rough sketch showing a thickness monitoring system,illustrating principally a forth thickness-measuring tool employed inthe system with first, second and third thickness-measuring tools,according to a modification of the second embodiment of the presentinvention;

FIG. 20 is a diagram that shows the transient variation in reflectedlight intensity in the fourth thickness-measuring tool (opto-acoustictype thickness-measuring tool) according to the modification of thesecond embodiment;

FIG. 21 is a flow chart showing the measurement procedure of the fourththickness-measuring tool (opto-acoustic type thickness-measuring tool)according to the second embodiment;

FIG. 22 is a data flow diagram showing the operation of the thicknessmonitoring system according to a modification of the second embodiment,which is adapted for executing in-line thickness monitoring of afour-layers structure; and

FIG. 23 is a data flow diagram showing the operation of the thicknessmonitoring system according to the third embodiment, which is adaptedfor executing in-line thickness monitoring of a three-layers structure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description specific details are set forth, such asspecific materials, process and equipment in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-knownmanufacturing materials, process and equipment are not set forth indetail in order not to unnecessary obscure the present invention.

Prepositions, such as “on”, “over”, “under”, “beneath”, and “normal” aredefined with respect to a planar surface of the substrate, regardless ofthe orientation in which the substrate is actually held. A layer is onanother layer even if there are intervening layers.

First Embodiment

As shown in FIG. 5, a thickness monitoring system according to a firstembodiment of the present invention encompasses a thickness-measuringtool 6 and a CIM server (measurement control server) 5. Thethickness-measuring tool 6 is connected to the CIM server 5 through acommunication network 4 such as local area network (LAN). Namely, thethickness monitoring system of the first embodiment is a control systemconfigured to control in-line monitoring of various thin films by asingle thickness-measuring tool 6 and the CIM server 5. Here, thevarious thin films may include silicon oxide (SiO₂) films grown bythermal oxidation or deposited by chemical vapor deposition (CVD),sputtering, vacuum evaporation processes; phosphosilicate glass (PSG)films, boro-phosphate-silicate glass (BPSG) film, silicon nitride(Si₈N₄) film, and poly-silicon films deposited by CVD; and metallicfilms deposited by CVD, sputtering, or vacuum evaporation processes.

A thickness memory 26, which stores the film thickness value of eachlayer of a multi-layer film, is connected to the CIM server (measurementcontrol server) 5. The thickness memory 26 records film thickness valuesT_(A, LP, WQ, Sr), T_(B, LP, WQ, Sr), T_(C, LP, WQ, Sr), . . . (p=1˜m;q=1˜n; r=1˜k) sorted into each lot, each wafer within each lot, and eachsite within each wafer, as shown in FIGS. 7A, 7B, 7C and 8.

The thickness-measuring tool 6 is a light interference typethickness-measuring tool that includes the optical system made up by alight source 11 that irradiates a white incident light hν_(i) to thesurface of a substrate 1, a spectroscope 12 that breaks up the reflectedlight, hν_(r) from the surface of the substrate 1 into differentcomponent wavelengths, and a photo detector 13 that detects theintensity of the reflected light at each resolved component wavelength,as shown in FIG. 5. It is acceptable to use well-known diffractiongrating type spectroscopes as well as prism type spectroscopes for thespectroscope 12. It is acceptable to use image sensors such as chargecoupled device (CCD) image sensors as the photo detector 13. Further,although illustration has been omitted from FIG. 5, it is a matter ofcourse that wafer stage and mechanism for driving the movement of waferstage that support a semiconductor wafer on which a first film 2 a, asecond film 2 b, a third film 2 c are laminated in this order. Also,although a sample having a three-layers structure is shown in FIG. 5, itis a matter of course that after measurement of the sample having onlythe first film 2 a deposited on the substrate 1, and after measurementof the sample having the first film 2 a and the second film 2 bdeposited on the substrate 1, the three-layers structure is measured, inview of the nature of the in-line monitoring.

The output of the photo detector 13 is connected to ameasuring-tool-side computer 3. Namely, the output of the photo detector13 is connected to a central processing unit (CPU) 21 or arithmeticprocessor through an input/output interface 27. The CPU (arithmeticprocessor) 21 includes a calculation module 22, which calculatestheoretical profiles (x: wavelength, y: intensity) of the reflectionspectrums, and a determination module 23, which compares actual measuredreflection spectrum detected by the photo detector 13 with theoreticalprofiles of the reflection spectrums, and decides film thickness.Further, a profile memory 24, which stores spectrums of reflected lightintensities detected by the photo detector 13, and a measurement recipememory 25, which stores a measurement recipe, are competed to the CPU21.

The measuring-tool-side computer 3 according to the first embodiment ofthe present invention further includes an input unit 28, which receivesinput such as data and commands from a user, and an output unit 29 thatprovides measurement results, as shown in FIG. 5. Although illustrationhas been omitted in FIG. 5, it is a matter of course that a data memorythat has stored desired data necessary to the calculation of thecalculation module 22, and a program memory that has stored filmthickness measurement control and calculation programs, are alsoincluded therein. The data memory can be made up by random access memory(RAM) that stores input/output data, film thickness measurementparameters, as well as history data and data occurring in the midst ofarithmetic computation, etc. The input unit 28 in FIG. 5 can be made ofelements such as a keyboard, a mouse, a light pen, or a flexible diskdevice. It is possible for an operator in control of film thicknessmeasurement to designate input output data, and set necessary parametersfrom the input unit 28. Further, through the input unit 28, it ispossible to set film thickness measurement parameters such as the formof input output data, and it is also possible to feed commands for theexecution or cessation of arithmetic computation. Also, printer devicesor display devices are included on the output unit 29. The output unit29 can display information such as input output data, measurementresults, or film thickness measurement parameters. Thethickness-measuring tool 6 in FIG. 5 shows a characteristic reflectionspectrum for a layered structure like that shown in FIGS. 9A to 9C, whenlight reflected from the surface of the substrate 1 interferes withlight reflected from interfaces of a multi-level film or interfacesbetween a film and the substrate 1. Because of this, the determinationmodule 23 determines a film thickness according to comparing theoreticalprofiles (x: wavelength, y: intensity) of the reflection spectrumscalculated by the calculation module 22 with a profile (x: wavelength,y: intensity) of the light intensity spectrum stored in the profilememory 24. The range of the wavelength used is 200 nm˜800 nm, as shownin FIGS. 9A to 9C, for example. For instance, measurement can be carriedout in a range from 20 nm to several dozen microns.

FIG. 6 is a dataflow diagram describing the operation of a thicknessmonitoring system according to the first embodiment, which is adaptedfar measuring the film thickness of a three-layers structure made up ofthe first film 2 a, the second film 2 b, and the third film 2 c. FIGS.7A, 7B, 7C and 8 are diagrams describing the details of the filmthickness data structure of the first film 2 a, the second film 2 b, andthe third film 2 c stored in the thickness memory 26.

The manufacturing process for semiconductor integrated circuits such asLSIs is generally carried out in units of lots. For example one lot ismade up of 25 wafers. For example, in a case of a 200 mm φ wafer, eachwafer has 9 to 13 measurement points (sites), and film thicknessmeasurement is carried out at sites therein that have been preappointed.

In the thickness monitoring system according to the first embodiment,data of the first film 2 a, the second film 2 b, and the third film 2 care sorted and stored in the thickness memory 26 of the CIM server(measurement control server) 5. However it is not necessarily essentialthat in-line monitoring is performed on all wafers of each lot, forexample, it is a matter of course that sampling testing by choosing arepresentational number of wafers out of the 25 wafers of making up alot, is also acceptable.

FIG. 7A shows a data structure where film thickness data of the firstfilm 2 a have been sorted and recorded in corresponding cells of atable, respectively. Each cell represents specific wafer in specificlot. For example, the film thickness values of a wafer 1, a wafer 2, awafer 3, . . . , a wafer n of a lot 1 are sorted and recorded asT_(A, L) ₁ _(, W) ₁ , T_(A, L) ₁ _(, W2), T_(A, L) ₁ _(, W3), . . .T_(A, L) ₁ _(, Wn). The film thickness values of a wafer 1, a wafer 2, awafer 3, . . . , a wafer n of a lot 2 are sorted and recorded asT_(A, L2, W) ₁ , T_(A, L2, W2), T_(A, L2, W3), . . . T_(A, L2, Wn). Thefilm thickness values of a wafer 1, a wafer 2, a wafer 3, . . . , awafer n of a lot 3 are sorted and recorded as T_(A, L3, W) ₁ ,T_(A, LS, W2), T_(A, L3, W3), . . . T_(A, L3, Wn). In the same manner,the film thickness values of a wafer 1, a wafer 2, a wafer 3, . . . , awafer n of a lot m are sorted and recorded as T_(A, Lm, W) ₁ ,T_(A, Lm, W2), T_(A, Lm, W3), . . . T_(A, Lm, Wn). Even morespecifically, the measured values are sorted into a plurality of sitesin each of the wafers, and recorded in the corresponding cells of thetable representing the specific site in the corresponding wafer,respectively, as shown in FIG. 8.

FIG. 7B shows film thickness data of the second film 2 b. For example,the film thickness values of the wafer 1, the wafer 2, the wafer 3, . .. , the wafer n of the lot 1 are sorted and recorded as T_(B, L) ₁_(, W) ₁ , T_(B, L) ₁ _(, W2), T_(B, L) ₁ _(, WS), . . . T_(B, L) ₁_(, Wn). The film thickness values of the wafer 1, the wafer 2, thewafer 3, . . . , the wafer n of the lot 2 are sorted and recorded asT_(B, L2, W) ₁ , T_(B, L2, W2), T_(B, L2, W3), . . . T_(B, L2, Wn). Thefilm thickness values of the wafer 1, the wafer 2, the wafer 3, . . . ,the wafer n of the lot 3 are sorted and recorded as T_(B, L3, W) ₁ ,T_(B, L3, W2), T_(B, L3, W3), . . . T_(B, L3, Wn). In the same manner,the film thickness values of the wafer 1, the wafer 2, the wafer 3, . .. , the wafer n of the lot m are sorted and recorded as T_(B, Lm, W) ₁ ,T_(B, Lm, W2), T_(B, Lm, W3), . . . T_(B, Lm, Wn). Even morespecifically, the measured values of each wafer are sorted into eachsite in the wafer and recorded, as shown in FIG. 8.

FIG. 7C shows film thickness data of the third film 2 c. For example,the film thickness values of the wafer 1, the wafer 2, the wafer 3, . .. , the wafer n of the lot 1 are sorted and recorded as T_(C, L) ₁_(, W) ₁ , T_(C, L) ₁ _(, W2), T_(C, L) ₁ _(, W3), . . . T_(B, L) ₁_(, Wn). The film thickness values of the wafer 1, the wafer 2, thewafer 3, . . . , the wafer n of the lot 2 are sorted and recorded asT_(C, L2, W) ₁ , T_(C, L2, W2), T_(C, L2, W3), . . . T_(C, L2, Wn). Thefilm thickness values of the wafer 1, the wafer 2, the wafer 3, . . . ,the wafer n of the lot 3 are sorted and recorded as T_(C, L3, W) ₁ ,T_(C, L3, W2), T_(C, L3, W3), . . . T_(C, L3, Wn). In the same manner,the film thickness values of the wafer 1, the wafer 2, the wafer 3, . .. , the wafer n of the lot m are sorted and recorded as T_(C, Lm, W) ₁ ,T_(C, Lm, W2), T_(C, Lm, W3), . . . T_(C, Lm, Wn). Even morespecifically, the measured values of each wafer are sorted into eachsite in the wafer and recorded, as shown in FIG. 8.

Further, it should be understood that the disclosure of FIGS. 7A, 7B, 7Cand 8 do not mean that data structures of the first embodiment must beconstructed by data, which are measured for all wafers of every lot inthe in-line monitoring. Namely, since it is acceptable to executesampling testing, by choosing a representational number of wafers out ofthe whole wafers making up a lot, it is possible to re-construct thedata structure shown in FIGS. 7A, 7B, 7C and 8 with skipping wafernumbers instead of sequential wafer numbers. And it is a matter ofcourse that is acceptable to execute sampling testing of specific lotsinstead of all lots.

A thickness monitoring method (in-line monitoring method) according tothe first embodiment will now be described while referencing datastructures shown in FIGS. 7A, 7B, 7C and 8 and flowcharts of FIGS. 10,11 and 12:

(a) First, the in a step S101 of FIG. 10, the substrate 1 is insertedinto the interior of a reaction tube (or chamber) of a CVD furnace, anda silicon oxide film (SiO₂ film) having a thickness of 100 nm is formedon the substrate 1 as the first film 2 a.

(b) Next, in a step S102, white incident light hν_(i) is emitted fromthe light source 11 of FIG. 5 so as to irradiate the substrate 1 havingthe first film 2 a formed thereon. Next, in a step S103, reflected lighthν_(r) from the substrate 1 is divided into component wavelengths by thespectroscope 12, which is implemented by a dispersing element such as aprism or grating. Further, the reflected light intensity of eachseparated wavelength is detected by the photo detector 13, sequentiallyin the order of resolved component wavelengths. Further, in a step S104,each of the light intensity detected sequentially by the photo detector13 is stored into the profile memory 24 of the measuring-tool-sidecomputer 3 so as to establish a profile of an actual measured reflectionspectrum (measured profile of optical spectrum). An example of theestablished profile of the actual measured reflection spectrum is shownin FIG. 9A. In FIG. 9A, abscissa represents the wavelength of thereflected light, and ordinate represents the reflected light intensity.Measurement is carried out at a plurality of predetermined measurementpoints (sites) on a surface of each wafer, each wafer inside each lot,because the irradiation sites are previously assigned on a surface ofeach wafer, respectively. Then, the actual measured reflection spectrums(measured profile of optical spectrums) are sorted and stored for eachlot, each wafer inside each lot, and each site inside each wafer.

(c) Next, in a step S105, a plurality of theoretical profiles of thereflection spectrums are calculated by the calculation module 22, whichis installed in the CPU 21 of the measuring-tool-side computer 3.Namely, a plurality of values that make up a range of candidate valuesof the film thickness of the first film 2 a are fed into the calculationmodule 22, and several theoretical profiles of the reflection spectrumsare arithmetically calculated by the calculation module 22. Thecalculations of these theoretical profiles of the reflection spectrumsare executed in plural based upon the plural candidate values of thefilm thickness in the film thickness range (ta˜ta+Δta) of the first film2 a that has been stored as the first measurement recipe in themeasurement recipe memory 25 of the measuring-tool-side computer 3.

(d) Next, in a step S106, a profile close to the actual measuredreflection spectrum of the first film 2 a stored in the profile memory24 is searched in the theoretical profiles of the reflection spectrumsobtained in the above mentioned step S105. Then the variable, upon whichthe closest theoretical profile of the reflection spectrum to the actualmeasured reflection spectrum is generated, is decided as the filmthickness T_(A) of the first film 2 a. Film thickness T_(A) isdetermined for each lot, each wafer inside of each lot, and each siteinside of each wafer.

(e) In a step S107, the film thickness T_(A) is stored as the filmthickness value T_(A, LP, WQ, Sr), for each lot (p=1˜m), each wafer(q=1˜n), and each site (r=1˜k) in the thickness memory 26 of the CIMserver (measurement control server) 5. Namely, film thickness values aresorted into each lot, and each wafer, and are stored into the thicknessmemory 26 in the data structure shown in FIG. 7A.

(f) Next in a step S111 of FIG. 11, using a CVD furnace, a siliconnitride film (Si₈N₄ film) having a thickness of 100 nm is formed on thefirst film 2 a as the second film 2 b.

(g) Afterward in a step S112, white incident light hν_(i) is irradiatedfrom the light source 11 of FIG. 5 onto the substrate 1 having thesecond film 2 b formed thereon. On the second film 2 b, the irradiationsites of the incident light hν_(i) toward the substrate 1 are aligned tothe corresponding irradiation sites of the first film 2 a in each waferinside each lot so that identical irradiation sites are irradiated. Thatis, the locations of the irradiation sites of the incident light hν_(i)toward the second film 2 b are also previously assigned on a surface ofeach wafer. In a step S113, the reflected light hν_(r) from thesubstrate 1 is divided into component wavelengths by the spectroscope12. Further, the reflected light intensity of each separated wavelengthis detected by the photo detector 13, sequentially in the order ofresolved component wavelengths. Afterward, in a step S114, the reflectedlight intensity detected by the photo detector 13 is measured for eachlot, each wafer inside of each lot, and each site inside of each wafer,and then stored In the profile memory 24 so as to establish a profile ofan actual measured reflection spectrum (measured profile of opticalspectrum). An example of the established profile of the actual measuredreflection spectrum is shown in FIG. 9B. FIG. 9B expresses a reflectionspectrum of the two-layers structure implemented by a silicon oxide filmwith a thickness of 100 nm and a silicon nitride film having a thicknessof 100 nm formed on the silicon oxide film, abscissa representswavelength of the reflected light and ordinate represents the reflectedlight intensity.

(h) Next in a step S115, the data of the film thickness valueT_(A, LP, WQ, Sr). of the underlying first film 2 a for each lot(p=1˜m), each wafer (q=1˜n), and each site (r=1˜k), that have beenstored into the thickness memory 26 of the CIM server (measurementcontrol server) 5, are read by the calculation module 22. Next in a stepS116, the calculation module 22 calculates a plurality of theoreticalprofiles of the reflection spectrums using the film thickness range(tb˜tb+Δtb) of the second film 2 b, which is the measurement subject,that has been stored in the second measurement recipe of the measurementrecipe memory 25. Namely, a plurality of thickness values that make up arange of candidate values of the film thickness of the second film 2 bare transferred into the calculation module 22, and several theoreticalprofiles of the reflection spectrums are arithmetically calculated bythe calculation module 22.

(i) Afterward, in a step S117, a profile close to the actual measuredreflection spectrum of the second film 2 b stored in the profile memory24 is searched in the theoretical profiles of the reflection spectrumsarithmetically calculated in the above mentioned step S116. Then thethickness value, upon which the closest theoretical profile of thereflection spectrum to the actual measured reflection spectrum isderived, is determined as the film thickness T_(B) of the second film 2b in the step S117. The film thickness T_(B) is stored as the filmthickness value T_(B, LP, WQ, Sr), for each lot (p=1˜m), each wafer(q=1˜n) and each site (r=1˜k) in the thickness memory 26 of the CIMserver (measurement control server) 5 in the step S118. Namely, filmthickness values are sorted into each lot (p=1˜m), each wafer (q=1˜n)and each site (r=1˜k), and are stored into the thickness memory 26 inthe data structure shown in FIG. 7B.

(j) Next in a step S121 of FIG. 12, using a CVD furnace, another siliconoxide film (SiO₂ film) having a thickness of 100 nm is formed on thesecond film 2 b as the third film 2 c.

(k) Afterward in a step S122, white incident light hν_(i) is irradiatedfrom the light source 11 of FIG. 5 onto the substrate 1 having the thirdfilm 2 c formed thereon. The irradiation sites of the incident lighthν_(i) toward the substrate 1 are predetermined for each lot, each waferinside each lot, and each site inside each wafer, corresponding toirradiation sites of the first film 2 a and the second film 2 b, so thatidentical points are irradiated. In a step S123, the reflected lighthν_(r) from the substrate 1 is divided into component wavelengths by thespectroscope 12. Further, the reflected light intensity of eachseparated wavelength is detected by the photo detector 13, sequentiallyin the order of resolved component wavelengths. Afterward, in a stepS124, the reflected light intensity detected by the photo detector 13 ismeasured for each lot, each wafer inside of each lot, and each siteinside of each wafer, and then stored in the profile memory 24 so as toestablish a profile of an actual measured reflection spectrum (measuredprofile of optical spectrum). An example of the established profile ofthe actual measured reflection spectrum is shown in FIG. 9C. FIG. 9Cexpresses a reflection spectrum of the three-layers structureimplemented by a silicon oxide film with a thickness of 100 nm, asilicon nitride film having a thickness of 100 nm formed on the siliconoxide film, and another silicon oxide film with a thickness of 100 nmformed on the silicon nitride film, abscissa represents wavelength ofthe reflected light and ordinate represents the reflected lightintensity.

(l) Next in a step S125, the data of underlying first film 2 a andsecond film 2 b for each lot (p=1˜m), each wafer (q=1˜n), and each site(r=1˜k), that have been stored into the thickness memory 26 of the CIMserver (measurement control server) 5, put more plainly, theT_(A, LP, WQ, Sr) (p=1˜m; q=1˜n; r=1˜k) of the first film 2 a, and theT_(B, LP, WQ, Sr) (p=1˜m; q=1˜n; r=1˜k) of the second film 2 b are readby the calculation module 22. Next in a step S126, the calculationmodule 22 calculates a plurality of theoretical profiles of thereflection spectrums using the film thickness range (tc˜tc+Δtc) of thethird film 2 c, which is the measurement subject, that has been storedin the third measurement recipe of the measurement recipe memory 25.Namely, a plurality of thickness values that make up a range ofcandidate values of the film thickness of the third film 2 c aretransferred into the calculation module 22, and several theoreticalprofiles are arithmetically calculated by the calculation module 22.

(m) Afterward, in a step S127, a profile close to the actual measuredreflection spectrum of the third film 2 c stored in the profile memory24 is searched in the theoretical profiles of the reflection spectrumsarithmetically calculated in the above mentioned step S126. Then thethickness value, upon which the closest theoretical profile of thereflection spectrum to the actual measured reflection spectrum isderived, is determined as the film thickness T_(C) of the third film 2c. The film thickness T_(C) is stored as the film thickness valueT_(C, LP, WQ, Sr), for each lot (p=1˜m), each wafer (q=1˜n), and eachsite (r=1˜k) in the thickness memory 26 of the CIM server (measurementcontrol server) 5. Namely, film thickness values are sorted into eachlot, and each wafer, and are stored into the thickness memory 26 in thedata structure shown in FIG. 7C.

According to the thickness monitoring method associated with the firstembodiment, for measuring film thickness of the top layer of amulti-layer structure, it is not necessary to measure the film thicknessof underlying layers at the same time as in earlier technology. Namely,in a case in measuring the film thickness of the three-layers structure,which is made up of the third film 2 c on the second film 2 b, thesecond film 2 b on the first film 2 a, the first film 2 a on thesubstrate 1, after the formation of the third film 2 c, it is onlynecessary to measure one layer of the third film 2 c. This is becauseall film thickness data underlying the true measurement subject layer ofthe third film 2 c, which is prescribed by the measurement range(tc˜tc+Δtc), the values T_(B) of the second film 2 b previously measuredat the time of its formation, and the values T_(A) of the first film 2 apreviously measured at the time of its formation, are read from the CIMserver (measurement control server) 5 in the calculation of thethickness of the true measurement subject layer. Therefore, a pluralityof theoretical profiles of the reflection spectrums are calculated forthe film thickness range (tc˜tc+Δtc) of the third film 2 c of aone-layer structure, which can be construed as if a single layer of thethird film 2 c is laminated on the substrate 1, and the period of timeof measurement, and measurement precision becomes equivalent to those ofa single layer.

Although description of the three-layers structure has been put forth asan example, the technical advantages of the thickness monitoring methodassociated with the first embodiment become more significant for themeasurement of multi-layer structure having more than four layers. Inrecent LSIs, multi-layer structures of above ten to thirteen layers havebecome commonplace, and using the thickness monitoring method associatedwith the first embodiment will achieve significant reductions inmeasurement time on multi-layer structure having particularly numerouslayers.

Also, according to the thickness monitoring method associated with thefirst embodiment, it is possible to suppress increases in manufacturingcosts because it becomes unnecessary to insert an extra semiconductorwafer for forming a subject thin film for the dedicated purpose of thein-line monitoring, in each of manufacturing stages where the subjectthin film of the corresponding level is formed, respectively. Andespecially the effectiveness of the significant suppression of increasesin manufacturing costs can be achieved by applying the thicknessmonitoring method of the first embodiment to multi-layer structurehaving particularly numerous layers.

Modification of the First Embodiment

In the thickness monitoring system shown in FIG. 5, thethickness-measuring tool 6 is connected to the CIM server (measurementcontrol server) 5 through the communication network 4 such as LAN.However, in certain cases is possible to organize a thickness monitoringsystem, in which data required for the determination of the thicknessare not transported through the communication network 4.

FIG. 13 shows a configuration of a thickness monitoring systemassociated with a modification of the first embodiment of the presentinvention, which has an organization in which the measuring-tool-sidecomputer 3 has the thickness memory 26, directly. The functions andoperations of the respective hardware components of the thicknessmonitoring system, such as the CPU 21 and the optical system (12, 13),which sends actual measured reflection spectrums (measured profile ofoptical spectrums) to the film thickness calculation apparatus(measuring-tool-side computer) 3 are substantially same as the thicknessmonitoring system shown in FIG. 5, and thus redundant description willbe omitted.

The thickness monitoring system according to the modification of thefirst embodiment, configured to perform the in-line thickness monitoringof a three-layers structure, operates in the substantially same mannerof the data flow diagram shown in FIG. 6. Because of this, operation canbasically be identical to that of the thickness monitoring system shownin FIG. 5, and thus can also achieve technical advantages that are alsoidentical to that of the thickness monitoring system shown in FIG. 5.Namely:

(a) First, the CPU 21 of the measuring-tool-side computer 3 determinesthe film thickness T_(A) of the first film 2 a, and stores this filmthickness T_(A) into the thickness memory 26 of the measuring-tool-sidecomputer 3 as T_(A, LP, WQ, Sr), sorted into each lot (p=1˜m), eachwafer (q=1˜n), and each site (r=1˜k).

(b) Next, after forming the second film 2 b on the first film 2 a theCPU 21 of the measuring-tool-side computer 3 reads the film thicknessvalue T_(A, LP, WQ, Sr), (p=1˜m; q=1˜n r=1˜k) from the thickness memory26. The CPU 21 then determines a film thickness T_(B) of the second film2 b and stores this film thickness T_(B) into the thickness memory 26 ofthe measuring-tool-side computer 3 as T_(B, LP, WQ, Sr), sorted intoeach lot (p=1˜m), each wafer (q=1˜n), and each site (r=1˜k).

(c) Next, after forming the third film 2 c on the second film 2 b, theCPU 21 of the measuring-tool-side computer 3 reads the film thicknessvalue T_(B, LP, WQ, Sr), (p=1˜m; q=1˜n; r=1˜k) from the thickness memory26. The CPU 21 then determines a film thickness T_(C) of the third film2 c and stores this film thickness T_(C) into the thickness memory 26 ofthe measuring-tool-side computer 3 as T_(C, LP, WQ, Sr), sorted intoeach lot (p=1˜m), each wafer (q=1˜n), and each site (r=1˜k).

In this manner, according to the thickness monitoring method (in-linemonitoring method) of the modification of the first embodiment, itbecomes possible to measure a multi-layer structure in the same amountof time it would take to measure a one-layer structure, with measurementprecision being equal to that of one-layer structure measurement, andwith lower measurement costs to around those of one-layer structuremeasurement These technical advantages are achieved by the similardataflow diagram as shown in FIG. 6, in which storing and reading of thefilm thickness data T_(A, LP, WQ, Sr), T_(B, LP, WQ, Sr),T_(C, LP, WQ, Sr) in and from the thickness memory 26 are executed witheach measurement recipe in the CPU 21, without employing the CIM server5 and the communication network 4.

Second Embodiment

As shown in FIG. 14, a thickness monitoring system according to a secondembodiment of the present invention encompasses a plurality ofthickness-measuring tools 6 a, 6 b, 6 c, . . . , a CIM server(measurement control server) 5, and a communication network 4 such asLAN to which the thickness-measuring tools 6 a, 6 b, 6 c, . . . and theCIM server are connected. Namely, in the thickness monitoring system ofthe second embodiment, the single CIM server (measurement controlserver) 5 controls the thickness-measuring tools 6 a, 6 b, 6 c, . . . .A first thickness-measuring tool 6 a, a second thickness-measuring tool6 b, and a third thickness-measuring tool 6 c, . . . executerespectively in-line thickness monitoring of miscellaneous thin filmformation processes of various thin films, which may include SiO₂ filmsgrown by steam (wet) oxidation, grown by dry oxidation, deposited byCVD, deposited by sputtering, deposited by vacuum evaporation; PSGfilms, BPSG firm, Si₈N₄ film, and poly-silicon films deposited by CVD;and metallic films deposited by CVD, sputtering, or vacuum evaporation.

Further, in FIG. 14, although measuring-tool-side computers are assumedto be installed respectively in the first thickness-measuring tool 6 a,the second thickness-measuring tool 6 b, and the thirdthickness-measuring tool 6 c, . . . , a system in which a commonmeasuring-tool-side computer is externally connected to the firstthickness-measuring tool 6 a, the second thickness-measuring tool 6 b,and the third thickness-measuring tool 6 c, . . . can achieve the samefunction and effectiveness. That is, employing a single measurementrecipe in the common measuring-tool-side computer, actual reflectionspectrums measured respectively by optical systems of the firstthickness-measuring tool 6 a, the second thickness-measuring tool 6 b,and the third thickness-measuring tool 6 c, . . . , are analyzedrespectively so as to determine corresponding film thicknesses for thefirst thickness-measuring tool 6 a, the second thickness-measuring tool6 b, and the third thickness-measuring tool 6 c, . . . .

All of the first thickness-measuring tool 6 a, the secondthickness-measuring tool 6 b, and the third thickness-measuring tool 6c, . . . can be implemented by same kinds of thickness-measuring tools,which operate with same principle of thickness measurement method, or athickness-measuring tool operating with different measurement principlefrom other thickness-measuring tools can be included partially in thethickness monitoring system of the second embodiment. It is alsoacceptable for all of the thickness-measuring tools to have differentmeasurement principles.

Therefore, for example, in the thickness monitoring system according tothe second embodiment, the first thickness-measuring tool 6 a and thesecond thickness-measuring tool 6 b are both described as being lightinterference type thickness-measuring tools, operating with the sameprinciple as in the first embodiment, and the third thickness-measuringtool 6 c is described as being a spectroscopic ellipsometer. Namely, ina case executing in-line thickness monitoring of a three-layersstructure, the measurement of the first film 2 a and the second film 2 bis carried out by light interference type thickness-measuring tools,while the measurements of the third film is carried out by thespectroscopic ellipsometer shown in FIG. 16.

The spectroscopic ellipsometer used for the third thickness-measuringtool 6 c includes a rotation-mechanism-equipped light polarizer 14 thatsets incident light hν_(i) from the light source 11 to a linearlypolarized light of a desired rotational angle (azimuth angle) θ aroundthe optical axis, and a light analyzer 15 that fixes the rotationalangle of the elliptical polarized light hν_(r) reflected from thesubstrate 1 around the optical axis and transmits the light. Thisconfiguration is different from the light interference typethickness-measuring tool shown in FIG. 5. The light source 11, being axenon (Xe) lamp or the like, the spectroscope 12 that breaks up lighttransmitted through the analyzer 15 into different componentwavelengths, and the photo detector 13, are all basically identical tothose of the light interference type thickness-measuring tool shown inFIG. 5, and thus redundant description thereof will be omitted. Also,the organization of the measuring-tool-side computer 3 of the secondembodiment is basically the same as the organization of themeasuring-tool-side computer 3 of the first embodiment, and thusredundant description thereof will be omitted.

As shown in FIG. 16, with the third thickness-measuring tool(spectroscopic ellipsometer) 6 c, incident light hν_(i) emitted from thelight source 11 being not polarized becomes linearly polarized lightwith a rotational angle (azimuth angle) θ after passing through thepolarizer 14, and incidents upon the surface of a sample at an incidentangle φ. In the second embodiment, although the sample is a three-layersstacked structure made up by the first film 2 a, the second film 2 b,and the third film 2 c, stacked on the substrate 1 in sequential order,it is not limited to the three-layers stacked structure. The rotationalangle (azimuth angle) θ is determined by the setting angle of thepolarizer 14. In the third thickness-measuring tool (spectroscopicellipsometer) 6 c, because the polarizer 14 and the analyzer 15 operatedin conjunction, the rotational angle θ is automatically determined bysetting the angle of the analyzer 15. On the other hand, the linearlypolarized incident light hν_(i) is reflected by the sample, changes ofintensity and phase occur, and the linearly polarized incident lightbecomes elliptical polarized light. This elliptical polarized reflectedlight hν_(r) passes through the analyzer 15 and is divided intocomponent wavelengths by the spectroscope 12. The analyzer 15 detectsthe variation of transmission intensity and the ellipso-parameter suchas the psi (ψ) and delta (Δ), which are caused by the rotation of thepolarizer 14 rotates, and using these ellipso-parameter, creates the tanψ like that shown in FIG. 17A, and the cos Δ like that shown in FIG.17B.

In FIG. 17A, abscissa represents wavelength λ, ordinate represents theratio of the P-polarized light intensity r_(p), and the S-polarizedlight intensity r_(s) of the reflected light hν_(r), as tan ψ. Namely,tan ψ is represented by the following equation:tan ψ=r _(p) /r _(s)  (1)In FIG. 17B, abscissa represents wavelength λ, ordinate represents thephase difference of the P-polarized light, and the S-polarized light ofthe reflected light hν_(r), as cos Δ. Namely, cos Δ is represented bythe following equation:cos Δ=(1/tan ψ)·M ₁ ·M ₂  (2)Here, M₁ represents a rotational parameter of the polarizer 14 with a2×2 matrix made of a first row (cos θ, sin θ) and a second row (sin θ,cos θ), and M₂ represents the reflection coefficient of a sample with a2×2 matrix made of a first row (r_(p), 0) and a second row (0, r_(s)).The change of polarization amount (ψ, Δ) between the incident lighthν_(i) and the reflected light hν_(r) is proportional to the product ofthe film thickness and the optical constant, thus it is possible toarithmetically calculate film thickness.

For the optical system of the third thickness-measuring tool(spectroscopic ellipsometer) 6 c, it is acceptable to use a combinationof the light polarizer 14 that sets incident light hν_(i) to a linearlypolarized light of a desired rotational angle around the optical axis,and the analyzer 15 that fixes reflected light hν_(r) from the substrate1 to a rotational angle around the optical axis and transmits the light,it is also acceptable to use a combination of the light polarizer 14that fixes the rotational angle around the optical axis and setsincident light hν_(i) to a linearly polarized light, and the analyzer 15that sets the reflected light hν_(r) from the substrate 1 to a desiredrotational angle around the optical axis and transmits the light.

FIG. 15 is a data flow diagram describing the operation of a thicknessmonitoring system according to the second embodiment in a case executingin-line thickness monitoring of a three-layers structure. Themeasurements of the first film 2 a and the second film 2 b are carriedout according to the procedures shown in FIGS. 10 and 11, but themeasurement of the third film 2 c is carried out according to theprocedure shown in FIG. 18. A film thickness measuring method (in-linemonitoring method) according to the second embodiment is describedbelow:

(a) First the first film 2 a is farmed on the substrate 1. With thethickness-measuring tool 6 a reflected light hν_(r) is divided intocomponent wavelengths by the spectroscope in the same manner as in thefirst embodiment, and light intensity detected by the photo detector isstored into the profile memory as a profile of an actual measuredreflection spectrum (measured profile of optical spectrum). A pluralityof theoretical profiles of the reflection spectrums are calculated bythe calculation module of the measuring-tool-side computer (theillustration is omitted from the FIG. 16, see the measuring-tool-sidecomputer 3 shown in FIG. 5) that is provided within the firstthickness-measuring tool 6 a. The calculations of these theoreticalprofiles of the reflection spectrums are executed for a plurality ofcandidate film thicknesses, which lie in the film thickness range of thefirst film 2 a (ta˜ta+Δta) that has been stored in the first measurementrecipe of the measurement recipe memory 25 of the measuring-tool-sidecomputer 3 (see FIG. 5). And one of candidate film thicknesses, uponwhich the closest theoretical profile of the reflection spectrum to theactual measured reflection spectrum stored in the profile memory isgenerated, is determined as a film thickness T_(A) for each lot, eachwafer, and each site, and this film thickness T_(A) is stored in thethickness memory 26 (see FIG. 16) of the CIM server (measurement controlserver) 5, as shown in FIG. 15.

(b) Next, the second film 2 b is farmed on the first film 2 a and thefilm thickness of the second film 2 b is determined using the secondthickness-measuring tool 6 b. In the determination of the film thicknessof the second film 2 b, as shown in FIG. 15, the measuring-tool-sidecomputer 3 (illustration omitted, see FIG. 5) installed in the secondthickness-measuring tool 6 b reads the underlying film thickness T_(A)stored in the thickness memory 26 of the CIM server (measurement controlserver) 5, and using the film thickness range (tb˜tb+Δtb) of the secondfilm 2 b, a plurality of theoretical profiles of the reflectionspectrums are calculated by the calculation module, and the filmthickness T_(B) is determined. Then, this film thickness T_(B) is storedin the in the thickness memory 26 of the CIM server (measurement controlserver) 5 as shown in FIG. 15.

(c) The third film 2 c is formed on the second film 2 b. In a step S201,incident light from the light source 11 of FIG. 16 irradiates thesubstrate 1, having the third film 2 c formed upon it, through thepolarizer 14 that sets incident light hν_(i) from the light source 11 toa linearly polarized light of a desired rotational angle (azimuth angle)around the optical axis. A plurality of irradiation sites of theincident light hν_(i) set to a rotation angle θ1 toward the substrate 1,which are assigned on a surface of each wafer, are aligned tocorresponding irradiation sites of the second film 2 b, so thatidentical sites are irradiated.

(d) The reflected light hν_(r) from the substrate 1 passes through theanalyzer 15. The analyzer 15 fixes the rotational angle of the reflectedlight hν_(r) around the optical axis. In a step S202, the reflectedlight hν_(r) passing through the analyzer 15 is divided into componentwavelengths by the spectroscope 12, and the intensity of the reflectedlight at each resolved component wavelength is detected by the photodetector 13, sequentially in the order of resolved componentwavelengths. A plurality of light intensities I1 detected sequentiallyby the photo detector 13, which corresponds to the rotation angle θ1,are stored into the profile memory 24.

(e) In a step S203, the processes of the steps S201˜S202 are repeatedfor the respective rotation angles θ2, θ3, . . . , θξ of the polarizer14, and corresponding wavelength dependence of the reflected lightintensities I1, I2, I3, . . . , Iξ. These sequence of the stepsS201˜S202 are repeated for each lot, each wafer inside of each lot, andeach side inside of each wafer.

(f) In a step S204, based upon the rotation angles θ1, θ2, θ3, . . . ,θξ of the polarizer 14, ellipso-spectrums (tan ψ, cos Δ) from thereflected light intensities I1, I2, I3, . . . , Iξ detected by the photodetector 13 are calculated and stored into the profile memory 24 asactual measured ellipso-spectrums (tan ψ, cos Δ). As examples of the setof profiles, the wavelength dependence of tan ψ shown in FIG. 17A, andthe wavelength dependence of cos Δ is shown in FIG. 17B for one ofrotation angles θ1, θ2, θ3, . . . , θξ.

(g) In a step S205, underlying film thickness data stored into thethickness memory 26, that is, the film thickness T_(A, LP, WQ, Sr),(p=1˜m; q=1˜n; r=1˜k) of the first film 2 a and the film thicknessT_(B, LP, WQ, Sr), (p=1˜m; q=1˜n; r=1˜k) of the second film 2 b, of eachlot (p=1˜m), each wafer (q=1˜n), and each site (r=1˜k), are read out.Then, the calculation module 22 calculates a plurality of theoreticalprofiles of the ellipso-spectrums (tan ψ, cos Δ) using the filmthickness range (tc˜tc+Δtc) of the third film 2 c.

(h) In a step S206, one of profiles close to the actual measuredellipso-spectrums (tan ψ, cos Δ) of the third film 2 c stored in theprofile memory 24 is searched in the theoretical profiles of theellipso-spectrums (tan ψ, cos Δ) arithmetically calculated in the abovementioned step S205. Then the thickness value, upon which the closesttheoretical profile of the ellipso-spectrums (tan ψ, cos Δ) to theactual measured ellipso-spectrums (tan ψ, cos Δ) is derived, isdetermined as the film thickness T_(C) of the third film 2 c. The filmthickness T_(C) is stored as the film thickness value T_(C, LP, WQ, Sr),for each lot (p=1˜m), each wafer (q=1˜n), and each site (r=1˜k) in thethickness memory 26 of the CIM server (measurement control server) 5.Namely, film thickness values are sorted into each lot, and each wafer,and are stored into the thickness memory 26 as shown in FIG. 15.

In this manner, according to a thickness monitoring method (in-linemonitoring method) associated with the second embodiment, it becomespossible to carryout thickness monitoring even in cases of multi-layerstructure in the same amount of time it would take to measure aone-layer structure, with measurement precision equaling that ofone-layer structure measurement precision, and lower measurement coststo around those of one-layer structure film thickness measurement costs.This is accomplished by bi-directional data transportation between theCIM server 5 and each of measuring-tool-side computer 3, which isinstalled in the first thickness-measuring tool 6 a, the secondthickness-measuring tool 6 b, the third thickness-measuring tool 6 c, .. . , respectively, in the same manner as shown in FIG. 15.

Modification of the Second Embodiment

The communication network 4 such as LAN can have a plurality ofthickness-measuring tools connected thereon, corresponding to manyprocess steps of the manufacturing processes of semiconductor devices.Put plainly, a thickness monitoring system according to a modificationof the second embodiment of the present invention is organized so thatthe plurality of thickness-measuring tool 6 a, 6 b, 6 c, 6 d . . . isconnected to CIM server (measurement control server) 5 through thecommunication network (LAN) 4.

As shown in FIG. 19, the thickness monitoring system according to themodification of the second embodiment further encompasses, besides thefirst thickness-measuring tool 6 a, the second thickness-measuring tool6 b, and the third thickness-measuring tool 6 c, a fourththickness-measuring tool 6 d configured to measure the film thickness ofa fourth film 2 d. On the modification of the second embodiment, thefourth thickness-measuring tool 6 d is an opto-acoustic typethickness-measuring tool. Namely, the thickness monitoring systemaccording to the modification of the second embodiment explains a casein which a metallic film 2 d is deposited as a fourth layer on thethree-layers structure described above, and the thickness of themetallic film 2 d is measured. It is acceptable that the measurementmethodology of the first thickness-measuring tool 6 a, the secondthickness-measuring tool 6 b, and the third thickness-measuring tool 6 cbe light interference type, spectroscopic ellipsometer, or some othertypes of film thickness measurement.

The opto-acoustic type thickness-measuring tool used as the fourththickness-measuring tool 6 d includes a probing laser (first lightsource) 51 configured to irradiate incident light hν_(i) (probe light)onto the surface of the sample having the fourth film (metallic film) 2d formed thereon, and an exciting laser (second light source) 52configured to irradiate incident light hν_(p) (excitation light) inpulse form overlapping with the incident light hν_(i) (probe light)irradiated from the probing laser 51, these features are different fromthe configuration of the light interference type thickness-measuringtools shown in FIG. 5. Further, in order that the reflected light fromthe surface of the sample having the fourth film (metallic film) 2 dformed thereupon can be detected, the photo detector 13 is provided inthe opto-acoustic type thickness-measuring tool.

The fourth thickness-measuring tool 6 d according to the modification ofthe second embodiment further embraces a measuring-tool-side computer 3d. The measuring-tool-side computer 3 d includes CPU 21 d, whichencompasses a calculation module 22 d configured to calculatetheoretical profiles of the reflection spectrums, and a determinationmodule 23 configured to compare actual measured reflection spectrumdetected by the photo detector 13 with theoretical profiles of thereflection spectrums, and decides film thickness. Further, a profilememory 24 d, which stores spectrums of reflected light intensitiesdetected by the photo detector 13, and a measurement recipe memory 25 d,which stores a measurement recipe, are connected to the CPU 21 d. Themeasuring-tool-side computer 3 d further includes an input unit 28 d,which receives input such as data and commands from a user, an outputunit 29 d that provides measurement results, and I/O interface 27 d. Theother organization and features of the measuring-tool-side computer 3 daccording to the modification of the second embodiment are basically thesame as those of the measuring-tool-side computer 3 shown in FIG. 5, andthus redundant description thereof will be omitted.

FIG. 22 is a data flow diagram describing the operation of a thicknessmonitoring system according to the modification of the second embodimentin a case executing in-line thickness monitoring in a situation havingthe metallic film 2 d deposited as the fourth layer on a three-layersstructure. The measurement of the first film 2 a, the second film 2 b,and the third film 2 c, is carried out in the same manner shown in thedata flow diagram of FIG. 15. Here, the measurement of only the fourthfilm 2 d will be described using the flowchart of FIG. 21, thusredundant description will be omitted. That is, the measurement of thefourth film 2 d of the thickness monitoring method (in-line monitoringmethod) according to the modification of the second embodiment isexecuted in the manner put forth below:

(a) A metallic thin film is formed as the fourth film 2 d on the thirdfilm 2 c using a sputtering process or a vacuum evaporation depositionprocess. In a step S301, incident light hν_(i) (probe light) from theprobing laser 51 is irradiated upon the sample having the fourth film(metallic film) 2 d formed thereon. The irradiation sites of theincident light hν_(i) toward the substrate 1 are previously assigned ona surface of each wafer, and sorted into each lot, each wafer insideeach lot, and each site inside each wafer, corresponding to irradiationsites of the first film 2 a to third film 2 c, so that identical sitesare irradiated. The photo detector 13 is set so that the light reflectedfrom each of the irradiation sites can be detected. The output from thephoto detector 13 is fed to profile memory 24 d so that data can hestored as actual measured reflection spectrums (measured waveform ofoptical spectrums) into the profile memory 24 d.

(b) In this situation, in a step S302, the incident light hν_(p)(excitation light) from the exciting laser 52 is irradiated overlappingthe irradiated incident light hν_(i) (probe light) from the probinglaser 51. The pulse of the incident light hν_(p) (excitation light) fromthe exciting laser 52 heats the fourth film (metallic film) 2 d,generating acoustic wave. The reflected light of the probing incidentlight hν_(i) (probe light) emitted from the probing laser 51, which isreflected in a period of time from the excitation time, when the pulseof the exciting incident light hν_(p) (excitation light) emitted fromthe exciting laser 52 is irradiated on the fourth film 2 d, manifeststhe attenuating profile (waveform) as shown in FIG. 20. FIG. 20illustrates a relationship between a sequence of intensity data ofreflected light originating from probe light hν_(i) irradiated upon thesurface of the fourth film 2 d, and the time after irradiation ofexcitation light hν_(p) on the fourth film 2 d so as to generate theacoustic wave in the fourth film 2 d. Therefore, the transient variationin the intensity of reflected light hν_(r) such as that shown in FIG. 20is stored into the profile memory 24 d as a profile (waveform) of anactual measured reflection spectrum (measured waveform of opticalspectrum).

(c) Next, underlying film thickness data stored into the thicknessmemory 26, that is, the film thickness T_(A, LP, WQ, Sr), (p=1˜m; q=1˜n;r=1˜k) of the first film 2 a, the film thickness T_(B, LP, WQ, Sr),(p=1˜m; q=1˜n; r=1˜k) of the second then film 2 b, and the filmthickness T_(C, LP, WQ, Sr), (p=1˜m; q=1˜n; r=1˜k) of the third film 2 cof each lot (p=1˜m), each wafer (q=1˜n), and each site (r=1˜k), are readout. Then in a step S303, the calculation module 22 d calculates aplurality of theoretical profiles (waveforms) of the reflectionspectrums using the film thickness range (tm˜tm+Δtm) of the fourth film(metallic film) 2 d, which is the measurement subject and is stored intoa fourth measurement recipe.

(d) In a step S304, one of profiles (waveforms) closest to the actualmeasured reflection spectrum of the fourth film (metallic film) 2 dstored in the profile memory 24 d is searched in the theoreticalprofiles (waveforms) of the reflection spectrums arithmeticallycalculated in the above mentioned step S303. Then the thickness value,upon which the closest theoretical profile (waveform) of the reflectionspectrum to the actual measured reflection spectrum is derived, isdetermined as the film thickness T_(D) of the fourth film (metallicfilm) 2 d for each lot (p=1˜m), each wafer (q=1˜n), and each site(r=1˜k). Then, as shown in FIG. 22, this film thickness value is storedinto the thickness memory 26 as the film thickness valueT_(D, LP, WQ, Sr), for each of the measured lots (p=1˜m), each of themeasured wafers (q=1˜n), and each of the measured sites (r=1˜k).

Third Embodiment

FIG. 23 is a data flow diagram describing operation of a thicknessmonitoring system according to a third embodiment of the presentinvention in a case executing in-line thickness monitoring of athree-layers structure. The thickness monitoring system according to thethird embodiment corresponds to a thickness monitoring system that is acombination of the first and second embodiments, as shown in FIG. 23.Namely, in a thickness monitoring method according to the thirdembodiment (in-line monitoring), a thickness-measuring tool 6 p acquirescommonly a plurality of actual measured reflection spectrums ofdifferent layers of thin films, such as the reflection spectrums of thefirst film 2 a and the second film 2 b. These actual measured reflectionspectrums are commonly processed by a common measuring-tool-sidecomputer 3 of the first thickness-measuring tool 6 p, and measurementvalues are arithmetically calculated for both of the first film 2 a andthe second film 2 b. On the other hand, a second thickness-measuringtool 6 q acquires exclusively an actual measured reflection spectrum ofa single layer of the third film 2 c, and the actual measured reflectionspectrum is exclusively processed by the measuring-tool-side computer 3of the second thickness-measuring tool 2 q, and a measurement value isarithmetically calculated.

(a) Namely, the first thickness-measuring tool 6 p determines filmthickness T_(A) of a first thin 2 a film and stores this film thicknessvalue T_(A) as T_(A, LP, WQ, Sr), sorted into each lot (p=1˜m), eachwafer (q=1˜n), and each site (r=1˜k), into the thickness memory 26 ofthe CIM server (measurement control server) 5, as shown in FIG. 23.

(b) Next, after the second film 2 b has been formed on the first film 2a, the first thickness-measuring tool 6 p reads out the film thicknessof value T_(A, LP, WQ, Sr), (p=1˜m; q=1˜n; r=1˜k) from the thicknessmemory 26 of the CIM server (measurement control server) 5, as shown inFIG. 23. Then, the film thickness T_(B) of the second film 2 b isdetermined, and is registered as T_(B, LP, WQ, Sr), sorted into each lot(p=1˜m), each wafer (q=1˜n), and each site (r=1˜k), into the thicknessmemory 26 of the CIM server (measurement control server) 5.

(c) Further, after the third film 2 c has been formed on the second film2 b the first thickness-measuring tool 6 p reads out the film thicknessof value T_(A, LP, WQ, Sr), (p=1˜m; q=1˜n; r=1˜k), andT_(B, LP, WQ, Sr), (p=1˜m; q=1˜n; r=1˜k) from the thickness memory 26 ofthe CIM server (measurement control server) 5, as shown in FIG. 23.Then, the film thickness T_(C) of the third film 2 c is determined, andis stored as T_(C, LP, WQ, Sr), sorted into each lot (p=1˜m), each wafer(q=1˜n), and each site (r=1˜k), into the thickness memory 26 of the CIMserver (measurement control server) 5.

In this manner, according to the thickness monitoring method (in-linemonitoring method) according to the third embodiment, it becomespossible to measure multi-layer structure in the same amount of time itwould take to measure a one-layer structure, with measurement precisionequaling that of one-layer structure measurement, and lower measurementcosts to around those of one-layer structure measurement. The aboveeffectiveness is achieved by the configuration which allows thebi-directional transport of data T_(A, LP, WQ, Sr), andT_(B, LP, WQ, Sr), between the measuring-tool-side computer 3 of thefirst thickness-measuring tool 6 p and the CIM server 5, and thebi-directional transport of data T_(A, LP, WQ, Sr), T_(B, LP, WQ, Sr),and T_(C, LP, WQ, Sr), between the measuring-tool-side computer 3 of thesecond thickness-measuring tool 6 q and the CIM server 5, as shown inFIG. 23.

Measurement Program

A computer implemented thickness monitoring method shown in FIGS. 10,11, 12, 18 and 21 can be executed within the thickness monitoringsystems shown in FIGS. 5, 13, 14, 16 and 19, being controlled bycomputer programs having algorithms identical to the flowcharts shown inFIGS. 10, 11, 12, 18 and 21. These computer programs can be stored inprogram memories (illustration is omitted) of the computer systemsimplementing the thickness monitoring systems of the first to thirdembodiment of the present invention.

Also, the computer program can be stored in a computer readable storagemedia, so as to allow the execution of a sequence of operations of thefilm measurement of the present invention, by reading the computerprogram of the film thickness monitoring from the computer readablestorage media. It here, the term “computer readable storage media” meanstorage devices capable of recording, such as external memory devices,semiconductor memory, magnetic disks, optical disks, magneto-optical(MO) disks, and magnetic tapes. More specifically, elements such asflexible disks, compact disk (CD)-ROM, cassette tape, and open reel tapeare included in the term “computer readable storage media”.

For example, the main unit of the CIM server (measurement controlserver) 5 can be organized so as to internally contain, or be able to beexternally connected to flexible disk devices (flexible disk drives),and optical disc devices (optical disk drives). It is possible toinstall a computer program that is stored on this storage media into theprogram memory implementing the thickness monitoring system, byinserting storage media into a flexible disk drive, in a case using aflexible disk drive, or a CD-ROM, in a case using an optical disk drive,and executing desired reading operation. If it is also possible to usememory devices such as ROM, which is used in video game cartridges forexample, or a cassette tape as a magnetic tape device, by connecting adesired drive device. Further, it is also possible to store the computerprogram into a remote program memory through communication network suchas the internet.

Semiconductor Device Manufacturing Method

Here, a semiconductor manufacturing method according to an embodiment ofthe present invention will be described using a complementarymetal-oxide-semiconductor (CMOS) integrated circuit as an example.Further, the semiconductor device manufacturing method and put forthherein below is only one example, and it is a matter of course thatthere are many other realizable manufacturing methods including thismodification.

(a) First, an n-type silicon wafer of about 2˜3 Ωcm with surfaceorientation of (100) plane is prepared as a semiconductor substrate 1. Athermal oxide film (SiO₂) of about 150 nm is formed an the surface ofthe semiconductors substrate 1. Afterward a photo resist film is coatedthereupon, and using a photolithography process, this photo resist filmis delineated to open a p-well formation region. Next, boron (B) ionsare implanted at a dose rate of about 10¹²-10¹⁸ cm⁻² into the p-wellformation region through the thermal oxide film. Next, part of thep-well formation region of the thermal oxide film is etched away. Thephoto resist film is removed, and after a desired cleaning process, theimplanted boron is activated and thermally diffused at approximately1200 degrees Celsius, forming a p-well.

(b) Next, the thermal oxide film formed on the main surface of thesemiconductor substrate 1 is removed completely. Then another thermaloxide film (SiO₂) having a thickness of about 100 nm is once againformed on the main surface semiconductor substrate 1. Afterward, asilicon nitride film (Si₃N₄) having a thickness of about 200 nm is grownusing a CVD process. A delineated photo resist pattern is formed on thesilicon nitride film using a photo lithography process, and reactive ionetching (RIE) is executed using the photo resist film as a mask so as toremove selectively the silicon nitride film of an element isolationformation region. Further, part of the main surface of the semiconductorsubstrate 1 is etched approximately 0.3 μm˜0.1 μm so as to form elementisolation groove in the element isolation formation region. A pluralityof active areas for arranging active elements, which are surrounded bythe element isolation region, are defined by the process. At thisprocess step, the active area is covered by the silicon nitride film.Afterward, the photo resist film used in the patterning of the siliconnitride film is removed. Impurity ions for the purpose of preventingchannel inversion are implanted into the bottom of the element isolationgroove by channel stop ion implantation. Further, an oxide film (SiO₂film) is buried in the element isolation groove using a CVD process.Afterward, using the silicon nitride film as a stopper, the main surfaceof the semiconductor substrate 1 is planarized using a chemicalmechanical polishing (CMP).

(c) Next, after removing the silicon nitride film, a dummy oxidationfilm with a thickness of about several dozen nanometers is formed in theactive area. Next, a plurality of gate threshold voltage control (Vthcontrol) ion implantations are carried out. In the Vth control ionimplantations, after covering nMOS transistor formation region with aphoto resist film using a photolithography process, the impurity ionsfar controlling pMOS gate threshold voltage are selectively implanted,and then, after covering pMOS transistor formation region with a photoresist film using a photolithography process, the impurity ions forcontrolling nMOS gate threshold voltage are selectively implanted. Afterremoving the dummy oxidation film, which have been used for protectingthe surface of the semiconductor substrate 1 during the Vth control ionimplantation, thermal oxidation is carried out so as to form a gateoxide film. This thermal oxidation corresponds to the step S101 of FIG.10, for example.

(d) Next in the step S102 of FIG. 10, the white incident light hν_(i)from the light source 11 of FIG. 5 is irradiated onto the semiconductorsubstrate 1 having the gate oxide film as the first film 2 a formedthereupon. In the step S103, light hν_(r) reflected from the surface ofthe semiconductor substrate 1 is divided into component wavelengths bythe spectroscope 12, and a plurality of reflection intensities aredetected by the photo detector 13, sequentially in the order of resolvedcomponent wavelengths at each resolved component wavelength. Then in thestep S104, a set of reflected light intensities detected by the photodetector 13 are stored into the profile memory 24 of themeasuring-tool-side computer 3 so as to establish a profile of an actualmeasured reflection spectrum (measured profile of optical spectrum). Inthe step S105, a plurality of theoretical profiles of the reflectionspectrums are calculated by the calculation module 22, which isinstalled in the measuring-tool-side computer 3. The calculations ofthese theoretical profiles of the reflection spectrums are executed inplural, at the film thickness range (ta˜ta+Δta) of the gate oxide film(the first film) 2 a that was stored in the first measurement recipe ofthe measurement recipe memory 25 of the measuring-tool-side computer 3.Then, one of the profiles closest to the actual measured reflectionspectrum of the gate oxide film (the first film) 2 a stored in theprofile memory 24 is searched in the theoretical profiles of thereflection spectrums obtained in the step S105. Then, in the step S106,the variable, upon which the closest theoretical profile of thereflection spectrum to the actual measured reflection spectrum isgenerated, is decided as the film thickness T_(A) of the gate oxide film(the first film) 2 a. In the step S107, the film thickness value T_(A)is stored in the thickness memory 26 to of the CIM server (measurementcontrol server) 5.

(e) Next, in the step S111 of FIG. 11, a poly-silicon film is formed onthe gate oxide film (the first film) 2 a as a second film 2 b using aCVD furnace. Afterward in the step S112, the white incident light hν_(i)is irradiated onto the semiconductor substrate 1 having the poly-siliconfilm (second film) 2 b formed thereupon. In the step S113, the lighthν_(r) reflected from the semiconductor substrate 1 is divided intocomponent wavelengths by the spectroscope 12 and a plurality ofreflection intensities are detected by the photo detector 13,sequentially in the order of resolved component wavelengths at eachresolved component wavelength. Afterward, in the step S114, a set ofreflected light intensities detected by the photo detector 13 are storedinto the profile memory 24 so as to establish a profile of an actualmeasured reflection spectrum (measured profile of optical spectrum). Inthe step S115, the underlying film thickness T_(A, LP, WQ, Sr), (p=1˜m;p=1˜n; r=1˜k) stored in the thickness memory 26 of the CIM server 5 isread out. In the step S116, the calculation module 22 calculates aplurality of theoretical profiles of the reflection spectrums using thefilm thickness range (tb˜tb+Δtb) of the poly-silicon film (second film)2 b that has been stored in the second measurement recipe of themeasurement recipe memory 25. Then, one of the profiles closest to theactual measured reflection spectrum of the poly-silicon film (secondfilm) 2 b stored in the profile memory 24 is searched in the theoreticalprofiles of the reflection spectrums obtained in the step S116. Then, inthe step S117, the variable, upon which the closest theoretical profileof the reflection spectrum to the actual measured reflection spectrum isgenerated, is decided as the film thickness T_(B) of the poly-siliconfilm (second film) 2 b. The film thickness T_(B) is stored as the filmthickness value T_(B, LP, WQ, Sr), for each lot (p=1˜m), each wafer(q=1˜n) and each site (r=1˜k) in the thickness memory 26 of the CIMserver (measurement control server) 5 in the step S118. Namely, filmthickness values T_(B, LP, WQ, Sr), of the poly-silicon film (secondfilm) 2 b are sorted into each lot (p=1˜m), each wafer (q=1˜n) and eachsite (r=1˜k), and are stored into the thickness memory 26 in the datastructure shown in FIG. 7B.

(f) A delineated photo resist pattern is formed on the poly-silicon film(second film) 2 b by a photolithography process. Then, using thedelineated photo resist film as a mask, the poly-silicon film (secondfilm) 2 b is selectively etched by dry etching processes such as RIE soas to form gate electrodes and poly-silicon wiring. Afterward the photoresist film is removed. Next, source and drain regions are selectivelyformed on the semiconductor substrate 1. First of all, the p-well, andthe top of the gate electrodes lying above the p-well are covered by anew photo resist film, using a photolithography process. Then using thepoly-silicon gate electrode as an implant stop, 10¹⁵ cm⁻² order p-typeimpurity ions such as boron (¹¹B⁺) ions are implanted into n-typeregions exposed at surfaces of active areas with self-aligned ionimplantation. In the p-type self-aligned ion implantation, p-typeimpurity ions are also implanted into the poly-silicon gate electrodes.Afterward, after removing the photo resist film, the tops of n-typeregions are covered with another photo resist film using aphotolithography process. Then using the poly-silicon gate electrode asa mask, 10¹⁵ cm⁻² order n-type impurity ions such as arsenic (⁷⁵As⁺)ions are implanted into p-wells exposed at surfaces of active areas withself-aligned ion implantation. In the n-type self-aligned ionimplantation, n-type impurity ions are also implanted into thepoly-silicon gate electrodes. Afterward, the photo resist firm isremoved. Next, the semiconductor substrate 1 is annealed so as toactivate the implanted ions, impurities are thermally diffused intosemiconductor substrate 1, and n type source and drain regions areformed in and at the surface of the p-wells, p-type source and drainregions in and at the surface of the n-type regions defined in theactive areas. Simultaneously, the p-type impurity ions and n-typeimpurity ions that have been implanted into the poly-silicon gateselectrodes are activated so that both poly-silicon gate electrodes onthe pMOS transistor side and the nMOS transistor side can manifest lowin resistance.

(g) Next, a first interlayer insulation film is deposited on thepoly-silicon gates electrodes (second film) 2 b as the third film 2 c byCVD process for the purpose of insulation between first level metallicinterconnections and the poly-silicon gates electrodes. The depositionof the first interlayer insulation film (the third film) 2 c correspondsto a step S121 in the flowchart of FIG. 12. Afterward, in a step S122,the white incident light hν_(i) is irradiated onto the semiconductorsubstrate 1 having the first interlayer insulation film (the third film)2 c formed thereupon. In a step S123, the light hν_(r) reflected fromthe semiconductor substrate 1 is divided into component wavelengths bythe spectroscope 12 and a plurality of reflection intensities aredetected by the photo detector 13, sequentially in the order of resolvedcomponent wavelengths at each resolved component wavelength. Afterward,in a step S124, a set of reflected light intensities detected by thephoto detector 13 are stored into the profile memory 24 so as toestablish a profile of an actual measured reflection spectrum (measuredprofile of optical spectrum).

(h) In a step S125, the underlying film thickness T_(A, LP, WQ, Sr),(p=1˜m; q=1˜n; r=1˜k) of the first film (gate electrode) 2 a, andT_(B, LP, WQ, Sr), (p=1˜m; q=1˜n; r=1˜k) of the second film(poly-silicon film) 2 b that has been stored into the thickness memory26 is read out. In a step S126, the calculation module 22 calculates aplurality of theoretical profiles of the reflection spectrums using thefilm thickness range (tc˜tc+Δtc) of the third film (first interlayerinsulation film) 2 c that has been stored in the third measurementrecipe. Then, one of the profiles closest to the actual measuredreflection spectrum of the third film (first interlayer insulation film)2 c stored in the profile memory 24 is searched in the theoreticalprofiles of the reflection spectrums obtained in the step S126. Then, ina step S127, the variable, upon which the closest theoretical profile ofthe reflection spectrum to the actual measured reflection spectrum isgenerated, is decided as the film thickness T_(C) of the third film(first interlayer insulation film) 2 c. In a step S128, the filmthickness T_(C) is stored in the thickness memory 26 as as the filmthickness value T_(C, LP, WQ, Sr), for each lot (p=1˜m), each wafer(q=1˜n) and each site (r=1˜k) in the thickness memory 26 of the CIMserver (measurement control server) 5. Namely, film thickness valuesT_(C, LP, WQ, Sr), of the third film (first interlayer insulation film)2 c are sorted into each lot (p=1˜m), each wafer (q=1˜n) and each site(r=1˜k), and are stored into the thickness memory 26 in the datastructure shown in FIG. 7C.

(i) Next, a delineated photo resist pattern is formed on the third film(first interlayer insulation film) 2 c using a photolithography process.RIE is then executed using the photo resist film as a mask, so as toopen contact holes within the third film (first interlayer insulationfilm) 2 c, thereby selectively exposing a part of the p-type source anddrain regions and the n-type source and drain regions at bottoms of thecontact holes. Further, a new delineated photo resist pattern is formedusing a photolithography process. RIE is then executed using the photoresist film as a mask, forming grooves (damascene grooves) used for thefirst level metallic interconnection. The interior of the contact holes,and the interior of the grooves (damascene grooves) are filled with acopper (Cu) film by plating. The surface of the third film (firstinterlayer insulation film) 2 c is then planarized using CMPplanarization, burying copper in interior of the contact holes, and theinterior of the grooves (damascene grooves) so as to form the firstlevel metallic interconnection.

(j) Next, a second interlayer insulation film 2 d is deposited on thefirst level metallic interconnection as the fourth film by a CVD processfor the purpose of insulation in between a second level metallicinterconnection and the first level metallic interconnection. Afterward,the white incident light hν_(i) is irradiated onto the semiconductorsubstrate 1 having the second interlayer insulation film (the fourthfilm) 2 d formed thereupon. The fight hν_(r) reflected from thesemiconductor substrate 1 is divided into component wavelengths by thespectroscope 12 and a plurality of reflection intensities are detectedby the photo detector 13, sequentially in the order of resolvedcomponent wavelengths at each resolved component wavelength. Afterward,a set of reflected light intensities detected by the photo detector 13are stored into the profile memory 24 as a profile of an actual measuredreflection spectrum (measured profile of optical spectrum). The filmthickness T_(A, LP, WQ, Sr), (p=1˜m; q=1˜n; r=1˜k) of the first film(gate electrode) 2 a, T_(B, LP, WQ, Sr), (p=1˜m; q=1˜n; r=1˜k) of thesecond film (poly-silicon film) 2 b, and T_(C, LP, WQ, Sr), (p=1˜m;q=1˜n; r=1˜k) of the third film (first interlayer insulation film) 2 cthat has been stored into the thickness memory 26 are read out. Thecalculation module 22 calculates a plurality of theoretical profiles ofthe reflection spectrums using the film thickness range (td˜td+Δtd) ofthe fourth film (second interlayer insulation film) 2 d that has beenstored in the fourth measurement recipe. Then, one of the profilesclosest to the actual measured reflection spectrum of the fourth film(second interlayer insulation film) 2 d stored in the profile memory 24is searched in the theoretical profiles of the reflection spectrums.Then, the variable, upon which the closest theoretical profile of thereflection spectrum to the actual measured reflection spectrum isgenerated, is decided as the film thickness T_(D) of the fourth film(second interlayer insulation film) 2 d. The film thickness T_(D) isstored in the thickness memory 26 as the film thickness valueT_(D, LP, WQ, Sr), for each lot (p=1˜m), each wafer (q=1˜n) and eachsite (r=1˜k) in the thickness memory 26 of the CIM server (measurementcontrol server) 5.

(k) Next, a delineated photo resist pattern is formed on the secondinterlayer insulation film (the fourth film) 2 d using aphotolithography process. RIE is then executed using the photo resistfilm as a mask, opening via holes within the second interlayerinsulation film (the fourth film) 2 d reaching to the first levelmetallic interconnection. Further, a new delineated photo resist patternis formed using a photolithography process. RIE is then executed usingthe photo resist film as a mask, forming grooves (second level damascenegrooves) used for the second level metallic interconnections. Theinterior of the via holes, and the interior of the second leveldamascene grooves are filled with a copper (Cu) film by plating. Thesurface of the second interlayer insulation film (the fourth film) 2 dis then planarized using CMP planarization, burying copper in interiorof the via holes, and the interior of the grooves (damascene grooves) soas to provide second level metallic interconnections.

(l) Next, a fifth, film (a third interlayer insulation film) isdeposited on the second level metallic interconnections by a CVD processfor the purpose of insulation in between third and second level metallicinterconnection. Next the film thickness values of the first throughfourth films are read out from the thickness memory 26 in the samemanner as in the determination of the first to fourth films. A pluralityof theoretical profiles of the reflection spectrums are calculated usingthe film thickness range of the fifth film (the third interlayerinsulation film) that was stored in a fifth measurement recipe. Then,one of the profiles closest to the actual measured reflection spectrumof the fifth film (the third interlayer insulation film) stored in theprofile memory 24 is searched in the theoretical profiles of thereflection spectrums. Then, the variable, upon which the closesttheoretical profile of the reflection spectrum to the actual measuredreflection spectrum is generated, is decided as the film thickness ofthe fifth film (the third interlayer insulation film). Then the filmthickness value is stored in the thickness memory 26.

From here on, while performing the similar in-line monitoring, asemiconductor device according to an embodiment of the present inventionis completed by necessary multi-level metallization process. Forexample, in the same manner as to first to fifth films, from the sixthfilm (fourth interlayer insulation film) to the ninth film (eighthinterlayer insulation film) can be stacked with repeating similarin-line monitoring methods. Using a CVD process, a passivation filmhaving a thickness of about 1 μm is deposited on the uppermost metallicwiring layer to prevent mechanical damage, and penetration of moistureand impurities. Films such as PSG film and silicon nitride film are usedas the passivation film.

According to a thickness monitoring method associated with embodiments,for measuring thickness of the top layer of a multi-layer structure, itis not necessary to measure the film thicknesses of underlying layers atthe same time as in earlier technology. Namely, for measuring the filmthickness of a j-layers structure implemented by a j-th film, a (j-1)thfilm, a (j-2)th film/ . . . /a second film/a first film/and thesubstrate 1, in the case that the only subject layer that needs to bemeasured is the uppermost later, it is not necessary to measure the(j-1)th film, the (j-2)th film/ . . . /the second film/the first film.This is accomplished by data bi-directional transportation between thethickness memory and the calculation module, and thicknesses data forunderlying layers can be provided from the thickness memory, which storethe thicknesses data for underlying layers after executing each of thein-line monitoring of the (j-1)th film, the (j-2)th film/ . . . /thesecond film/the first film, at respective process steps.

Therefore, the theoretical profile of the reflection spectrum of upperlayer can be calculated as if the thickness of a one-layer structure,such that a first film is deposited on the substrate, is calculated andthe measurement time period, and measurement precision becomesequivalent to that in a case measuring the film thickness of a singlelayer.

In recent LSI, multi-layer structure of above ten to thirteen layershave become commonplace, and according to the thickness monitoringmethod associated with the embodiment of the present invention, asignificant reduction in measurement time of the multi-layer structurehaving particularly numerous layers is achieved. Also, according to athickness monitoring method of the embodiments, it is possible tosuppress increases in manufacturing costs because it becomes unnecessaryto insert extra semiconductor wafers for the dedicated purpose ofin-line monitoring, in each of the process steps where each of thinfilms is formed. And, according to a thickness monitoring method of theembodiments, significant effectiveness of suppression of increases inmanufacturing costs can be achieved for a multi-layer structure havingparticularly numerous layers.

Other Embodiments

Various modifications will become possible for those skilled in the artafter receiving the teaching of the present disclosure without departingfrom the scope thereof. Thus, the present invention of course includesvarious embodiments and modifications and the like which are notdetailed above. Therefore, the scope of the present invention will bedefined in the following claims.

1. A computer program product tangibly embodied on a computer readablemedium containing instructions for controlling an in-line monitoringsystem so as to execute a sequence of successive monitorings ofrespective thicknesses of a subject uppermost film deposited on anunderlying multi-layer structure in each of a plurality of manufacturingstages, the underlying multi-layer structure comprising a plurality ofthin films formed on a substrate by previous manufacturing stages, themonitoring system having a thickness memory for storing the thicknessdata of each of the thin films of the underlying multi-layer structure,the thickness data being determined before the subject uppermost film isformed on the underlying multi-layer structure, the computer programproduct including a plurality of sub-programs, each of the sub-programsbeing configured to determine only a corresponding thickness of thesubject uppermost film at one of the plurality of manufacturing stages,the sub-program corresponding to a subject manufacturing stagecomprising: instructions configured to measure an optical spectrumprofile of the subject uppermost film formed on the underlyingmulti-layer structure; instructions configured to read the thicknessdata of each of the thin films of the underlying multi-layer structurefrom the thickness memory; instructions configured to calculate aplurality of theoretical optical spectrum profiles of the subjectuppermost film based upon corresponding candidate film thicknesses ofthe subject uppermost film, using a measurement recipe for the subjectuppermost film and the thickness data of each of the thin films of theunderlying multi-layer structure; and instructions configured to searchone of the theoretical profiles of the optical spectrum of the subjectuppermost film, which is closest to the measured optical spectrumprofile of the subject uppermost film so as to determine a thickness ofthe subject uppermost film by the closest theoretical profile.
 2. Thecomputer program product of claim 1, wherein the underlying multi-layerstructure comprises a first film formed on the substrate and a secondfilm formed on the first film, the thickness memory storing thethickness data of the first film, the thickness data being determinedbefore the second film is formed on the first film, wherein asub-program for determining the thickness data of the second filmcomprises: instructions configured to measure an optical spectrumprofile of the second film after the second film is formed on the firstfilm; instructions configured to read the thickness data of the firstfilm from the thickness memory; instructions configured to calculate aplurality of theoretical optical spectrum profiles of the second filmbased upon corresponding candidate film thicknesses of the second film,using a measurement recipe for the second film and the thickness data ofthe first film; and instructions configured to search one of thetheoretical optical spectrum profiles of the second film, which isclosest to the measured optical spectrum profile of the second film soas to determine a thickness of the second film by a closest theoreticalprofile of the second film.
 3. The computer program product of claim 2,wherein a sub-program for determining the thickness data of the firstfilm comprises: instructions configured to measure an optical spectrumprofile of the first film; instructions configured to calculate aplurality of theoretical optical spectrum profiles of the first filmbased upon corresponding candidate film thicknesses of the first film,using a measurement recipe for the first film; and instructionsconfigured to search one of the theoretical optical spectrum profiles ofthe first film, which is closest to the measured optical spectrumprofile of the first film so as to determine a thickness of the firstfilm by a closest theoretical profile of the first film.
 4. The computerprogram product of claim 1, wherein the measured optical spectrumprofile is established by a relationship between a sequence of intensitydata of reflected light originating from white light irradiated upon asurface of the subject uppermost film, and component wavelengths of thereflected light.
 5. The computer program product of claim 1, wherein themeasured optical spectrum profile is established by a relationshipbetween a sequence of ellipso-parameter data of reflected lightoriginating from polarized white light irradiated upon a surface of thesubject uppermost film, and the component wavelengths of the reflectedlight, the ellipso-parameter data changes in light polarization inducedby reflection of the light.
 6. The computer program product of claim 1,wherein the measured optical spectrum profile is established by arelationship between a sequence of intensity data of reflected lightoriginating from probe light irradiated upon a surface of the subjectuppermost film, and an attenuation of an acoustic wave generated in thesubject uppermost film by an irradiation of exciting light on thesubject uppermost film.